Question

How do I answer this question on khan academy.

Answer 1

If $b$ is Ben's age and $i$ is Ishaan's age, then

• present day: $b=4i$
• 6 years ago: $b-6=6(i-6)$

Rewrite the second equation as

$b-6=6(i-6)\implies b-6=6i-36\implies b+30=6i$

Substitute $b=4i$ into this equation to solve for $i$:

$b+30=6i\implies4i+30=6i\implies30=2i\implies i=15$

Then

$b=4i\implies b=4\cdot15=60$

So Ben is 60 years old now.